Elevator drive machine

ABSTRACT

An elevator drive machine includes a traction sheave and an electromechanical apparatus having at least two electric motors for driving the traction sheave. The traction sheave and the weight applied to it via the elevator ropes are supported by bearings between the stators and rotors of the electric motors driving the traction sheave of the drive machine.

This application is a Continuation of PCT International Application No.PCT/FI98/00059 filed on Jan. 22, 1998, which designated the UnitedStates and on which priority is claimed under 35 U.S.C. § 120, theentire contents of which are hereby incorporated by reference.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to an elevator drive machine.

2. Description of the Related Art

The drive machine of a traction sheave elevator has a traction sheavewith grooves for the hoisting ropes of the elevator and an electricmotor driving the traction sheave either directly or via a transmission.Traditionally the electric motor used to drive an elevator has been ad.c. motor, but increasingly a.c. motors, such as squirrel-cage motorswith electronic control are being used. One of the problems encounteredin gearless elevator machines of conventional construction has beentheir large size and weight. Such motors take up considerable space andare difficult to transport to the site and to install. In elevatorgroups consisting of large elevators, it has sometimes even beennecessary to install the hoisting machines of adjacent elevators ondifferent floors to provide enough room for them above the elevatorshafts placed side by side. In large elevator machines, transmitting thetorque from the drive motor to the traction sheave can be a problem. Forexample, large gearless elevators with a conventional drive shaftbetween the electric motor and the traction sheave are particularlysusceptible to develop significant torsional vibrations due to torsionof the shaft.

Recently, solutions have been presented in which the elevator motor is asynchronous motor, especially a synchronous motor with permanentmagnets. For example, the specification of WO 95/00432 presents asynchronous motor with permanent magnets which has an axial air gap andin which the traction sheave is directly connected to a disc forming therotor. Such a solution is advantageous in elevator drives with arelatively low torque requirement, e.g. a hoisting load of about 1000kg, and in which the elevator speed is of the order of 1 m/s. Such amachine provides a special advantage in applications designed tominimize the space required for the elevator drive machine, e.g. inelevator solutions with no machine room.

The specification of FI 93340 presents a solution in which the tractionsheave is divided into two parts placed on opposite sides of the rotorin the direction of its axis of rotation. Placed on both sides of therotor are also stator parts shaped in the form of a ring-like sector,separated from the rotor by air gaps.

In the machine presented in the specification of FI 95687, the rotor andthe stator parts on either side of it with an air gap in between arelocated inside the traction sheave. In this way, the traction sheave isintegrated with the rotor, which is provided with magnetizing elementscorresponding to each rotor part.

The specification of DE 2115490 A presents a solution designed to drivea cable or rope drum or the like. This solution uses separate linearmotor units acting on the rim of the drum flanges.

For elevators designed for loads of several thousand kg and speeds ofseveral meters per second, none of the solutions presented in theabove-mentioned specifications is capable of developing a sufficienttorque and speed of rotation. Further, problems might be encountered inthe control of axial forces. In motors with multiple air gaps, furtherdifficulties result from the divergent electrical and functionalproperties of the air gaps. This imposes special requirements on theelectric drive of the motor to allow full-scale utilization of themotor. Special requirements generally result in a complicated system ora high price, or both.

The specification of GB 2116512 A presents a geared elevator machinewhich has several relatively small electric motors driving a singletraction sheave. In this way a machine is achieved that needs only arelatively small floor area. The machine presented in GB 2116512 A canbe accommodated in a machine room space not larger than thecross-sectional area of the elevator shaft below it. Such anadvantageous machine room solution has not been usable in the case oflarge gearless elevators because these typically have a machine with onelarge motor that extends a long way sideways from the traction sheave.The specification of EP 565 893 A2 presents a gearless elevator machinecomprising more than one modular motor unit, which are connectedtogether to drive traction sheaves also connected together. In such asolution, the length of the machine increases as its capacity isincreased by adding a motor module. The problem in this case is that thelength of the machine is increased on one side of the traction sheave,which is why the machine extends beyond the width of the elevator shaftbelow. Supporting and stiffening such a long machine so that its ownweight and the rope suspension will not produce harmful deformations islikely to result in expensive and difficult solutions. For instance, thebending of a long machine requires a special and expensive bearingsolution. If bending or other forms of load produce even the slightestflattening of the traction sheave to an elliptical shape, this willprobably lead to vibrations that reduce the travelling comfort providedby the elevator.

SUMMARY OF THE INVENTION

It is an object of the present invention to achieve a new gearlesselevator drive machine which develops a torque, power and rotationalspeed preferably as needed in large and fast elevators. Morespecifically, the invention is directed to a gearless elevator drivemachine that includes a traction sheave and an electromechanicalapparatus having two electric motors, each having a rotor and a stator,for driving rotation of the traction sheave. The traction sheave ispositioned between the rotors of the two electric motors along an axisof rotation of traction sheave. The traction sheave, and weight appliedthereto via elevator ropes attached to an elevator car and acounterweight substantially supported in the radial direction oftraction sheave by bearings radially positioned between stators androtors of the electric motors.

With the solution of the present invention, the torque is developed bymeans of two motors or motor blocks, the torque being thus doubled ascompared with a single motor. The axial forces generated by the twomotor blocks compensate each other, thus minimizing the strain-on thebearings and motor shaft.

With the drive machine of the present invention, due to the good torquecharacteristics of the machine, a large traction sheave size in relationto the size, performance and weight of the drive machine is achieved.For instance, an axle load of 40000 kg can be handled by a machineweighing below 5000 kg, even if the elevator speed is as high as 9 m/sor considerably higher.

As the structure of the drive machine allows large rotor and statordiameters in relation to the traction sheave diameter, a sufficienttorque on the traction sheave is easily generated. On the other hand, ashort distance between the bearings in the direction of the axis ofrotation automatically ensures small radial deflections, so that noheavy structures are needed to prevent such deflections.

Especially in the case of elevator drive machines with the highestrequirements regarding load capacity, having a single traction sheavedriven by at least two motors helps obviate the relatively high costs inrelation to load capacity of large individual motors. By placing thetraction sheave between two motors, a compact machine structure isachieved, as well as a possibility to transmit the torque, power andforces directly from the machine to the traction sheave without aseparate drive shaft. By coupling the rotors of two different electricmotors mechanically together with the traction sheave, these advantagesare achieved to a distinct degree.

The very close integration of the rotor parts of the motor with thetraction sheave results in a machine in which the rotating partspractically function as a single block, allowing improved accuracy inthe control of elevator movements.

As the frame of the drive machine is used both as a shell of themotor/motors and as a carrier of the bearings of the moving parts, thetotal weight of and the space required by the machine are relatively lowas compared with conventional hoisting machines designed forcorresponding use.

In principle, bearings are only needed for each rotor, whose bearingboxes are easy to seal. Any lubricant that may pass through the sealingcan easily be so guided off that it will cause no harm.

Because the traction sheave is attached substantially to the junctionbetween the rotor blocks or because the traction sheave joins the rotorblocks together along a circle of a fairly large radius, the torquedeveloped by the motor is transmitted directly from the rotor to thetraction sheave.

In the drive machine of the invention, the air gaps can be adjusted inpairs so that they will be of equal size, and the mutual air gap sizesof the two motors/motor blocks can even be adjusted so that themotors/motor blocks will look the same to the electric drive. In thisway it is possible to have two motors/motor blocks driven by a singleelectric drive without incurring differences in the behavior of themotors/motor blocks due to the drive machine being driven by a singleelectric drive.

Due to its small size and light weight with regard to its load capacity,the machine is easy to implement in terms of both machine room lay-outand in respect of installation. Elevator machines with a high loadcapacity are often used in elevator groups comprising several elevators.As the hoisting machine can be accommodated in a machine room floor areathe size of the cross-section of the elevator shaft below it, thisprovides a great advantage in respect of utilization of building space.

BRIEF DESCRIPTION OF DRAWINGS

In the following, the invention will be described by the aid of anexample, which in itself does not constitute a limitation of the rangeof application of the invention, and by referring to the attacheddrawings, in which

FIG. 1 presents an elevator drive machine as provided by the presentinvention, seen from the axial direction;

FIG. 2 presents the drive machine of FIG. 1 in side view and partiallysectioned;

FIG. 3 presents a more detailed view of the drive machine shown in FIG.2;

FIG. 4 presents the drive machine of FIG. 1 in top view;

FIG. 5 illustrates the placement of the drive machine of the presentinvention;

FIG. 6 presents a cross-section of another drive machine according tothe present invention, and

FIG. 7 presents a more detailed view of the drive machine as shown inFIG. 6.

DETAILED DESCRIPTION

FIG. 1 shows a gearless drive machine 1 as provided by presentinvention, seen from the axial direction. The figure shows the outline 2a of the traction sheave 2 of the drive machine 1 to illustrate theplacement of the traction sheave in relation to the frame block 3forming part of the frame of the machine. The frame block 3 ispreferably made by casting, preferably as a cast iron block. The frameblock can also be manufactured e.g. by welding from pieces of steelsheet. However, a welded frame block can probably be only used inspecial cases, e.g. when a very, large machine is to be manufactured asan individual case. Even a frame block as high as about 2 m can beadvantageously made by casting if a series of several machines is to beproduced.

The frame block is stiffened by a finning 44. The finning is partlyannular, including one or more rings, and partly radial. The radialparts of the finning are directed from the central part of the frameblock 3 towards attachment points 4,5,6,7,8 provided along the edge ofthe frame block and towards the mountings 10 of the operating brakes 9of the elevator and the legs 11 of the drive machine, by which the drivemachine is fixed to its base. The legs 11 are located near theattachment points 6,7 in the lower part of the frame block. The frameblock has seats for a fan 12 and a tachometer 13 with the requiredopenings. The traction sheave bearings are behind a cover 15. The coveris provided with a duct for the adjusting screw 16 of a device for axialpositioning of the traction sheave. The cover 15 is also provided with afilling hole 42 for the addition of lubricant into the bearing space andan inspection hole or window 41 for the inspection of the amount oflubricant.

FIG. 2 presents the drive machine 1 in a partially sectioned side view.FIG. 3 presents details of the drive machine shown in FIG. 2, showingthe bearing arrangement more clearly. In these figures, the part to theright of the center line-of the machine shows section A—A of FIG. 1,while the part to the left shows section R—R of FIG. 1. It is largely aquestion of definition whether the figure represents a drive machine inwhich the traction sheave is placed in a motor which has a rotor andstator divided into blocks, between the two rotor blocks 17,18 of themotor and attached to these, or whether the figure represents two motorsbetween which the traction sheave 2 is attached to the rotors 17,18 ofthe motors. The stators/stator blocks 19,20 are fixed to the frameblocks 3,3 a. Air gaps are provided between the stators and rotors. Theair gaps in the motors shown in the figures are so-called axial airgaps, in which the flux direction is substantially parallel to the motoraxis. The stator winding is preferably a so-called slot winding. Therotor magnets 21 are preferably permanent magnets and attached to therotors 17,18 by a suitable method. The magnetic flux of the rotor passesthrough the rotor disc 17,18. Thus, the part of the rotor disc that liesunder the permanent magnets acts both as a part of the magnetic circuitand as a structural member of the rotor. The permanent magnets may be ofdifferent shapes and may be divided into component magnets placed sideby side or one after the other. The rotor disc is preferablymanufactured by casting from cast iron. Both the rotor disc and theframe blocks are preferably shaped so that they fit together withanother identical body, so that it will not be necessary to produce apart and a counterpart separately. The rotor 17,18 is provided withroller bearings 22 supporting it on the corresponding frame block 3 a,3.The roller bearings 22 support the radial forces. In very largeelevators, the bearings have to carry a weight of tens of tons, becausein many cases almost all of the weight of both the elevator car and thecounterweight is applied via the elevator ropes to the traction sheave.The elevator ropes and compensation ropes or chains also significantlyincrease the weight. Axial net forces are received by an auxiliarybearing 40. Using an axial adjustment associated with the auxiliarybearing 40, the rotors 17,18 are centered so that each stator-rotor pairwill have an equal air gap.

The traction sheave and the rotor blocks are attached to each other toform the rotating part of the machine, supported by bearings on theframe blocks. The auxiliary bearing 40, attached by its cage to therotor, and the screw 16, which engages the bearing boss and is supportedby the cover 15, act as an adjusting device in the bearing housing,designed to move the motor blocks in the axial direction. When the screw16 is turned, it pushes or pulls the whole rotating part, depending onthe turning direction. Since the rotor magnets in each rotor block tendto pull the rotating part towards the stator corresponding to the rotorin question and since the stators and rotors, respectively, areidentical, the center-position can be found by turning the adjustingscrew until the pushing and pulling force of the screw is practicallynil. A more accurate method of finding the center position is by turningthe rotating part and measuring the electromotive force obtained fromthe stators. When, as the rotating part is revolved, the electromotiveforce measured from the first stator block and that measured from thesecond stator block are entered the same, the rotating part has beensuccessfully centered. In this way, both stator-rotor pairs have veryconsistent drive characteristics and they can be driven by a singleelectric drive without one of the stator-rotor pairs being subjected toa higher load than the other.

The stator 19,20 together with its winding is attached by means offixing elements to the frame block 3 a,3, which, on the one hand, actsas a mounting that holds the stator in position and, on the other hand,as the shell structure of the motor and the drive machine as a whole.The fixing elements are preferably screws. Attached to the rotor 17,18are rotor excitation devices placed opposite to the stators. Theexcitation devices are formed by fixing a number of permanent magnets 21in succession to the rotor so that they form a ring.

The stator 19,20 together with the stator windings is attached withfixing elements to the frame block 3 a,3, which acts both as a base forholding the stator in place and as a shell structure for the entiredrive machine. The fixing elements are preferably screws. The rotor17,18 is provided with rotor excitation devices mounted opposite to thestators. The excitation devices have been formed by attaching to therotor a series of permanent magnets 21 in succession so that they form acircular ring.

Between the permanent magnets and the stator there is an air gap whichis substantially perpendicular to the axis of rotation of the motor. Theair gap may also be somewhat conical in shape, in which case the centerline of the cone coincides with the axis of rotation. As seen in thedirection of the axis of rotation, the traction sheave 2 and the stator19,20 are placed on opposite sides of the rotor 17,18.

Between the frame blocks 3 a,3 and the rotors 17,18 there are ring-likecavities in which the stator and the magnets are placed.

The outer edges of the rotors 17,18 are provided with braking surfaces23,24, which are engaged by the brake shoes 25 of the brakes 9.

The rotor blocks are provided with aligning elements by means of whichthe permanent magnets of the first and second rotors can be positioned.The permanent magnets are mounted in an arrow pattern. The magnets canbe aligned either directly opposite to each other or with a slightoffset. As the rotors are of identical design, placing them in pairsopposite to each other means that while the first one is rotatingforward, the second one is, as it were, rotating backward if the slotwindings in the opposite stators are mounted in a mirror imagearrangement. This eliminates any possible structural dependence of theoperating characteristics of the motor on the direction of rotation. Therotor magnets can also be implemented with the arrow figures pointing tothe same direction of rotation. The aligning elements are bolts, thenumber of which is preferably divisible by the number of poles and whosepitch corresponds to the pole pitch or its multiple.

FIG. 4 shows the drive machine 1 in top view. The connecting pieces 5b,8 b on the sides of the drive machine which connect the attachmentpoints 5,5 a,8,8 a of opposite frame blocks are clearly visible, and sois the connecting piece 4 b on the top side of the drive machine whichconnects the attachment points 4,4 a provided in the top parts of theframe blocks. The top connecting piece 4 b is of a stronger constructionthan the other connecting pieces. This top connecting piece 4 b isprovided with a loop 43 by which the drive machine can be hoisted. InFIG. 4, the outline of the wall of the elevator shaft 39 below the drivemachine is depicted with a broken line. The drive machine is clearlyinside this outline. This means a space saving in the building. As themachine is completely contained in the space directly above the elevatorshaft, the machine room arrangements above an elevator bank will besimple. Even when the cross-section of the machine room is the same sizeand shape as the cross-section of the elevator shaft, there will beenough space left over in the machine room around the drive machine toallow all normal service and maintenance operations to be carried out.

By placing the legs 11 near the lower edges of the machine, a maximumstability of the machine when mounted and fixed to its support isachieved. The legs are preferably located substantially outside theplanes defined by the stator and rotor blocks.

FIG. 5 illustrates the way in which the drive machine 1 is placed in themachine room 45. The drive, machine is mounted on a support 46constructed of steel beams. Using a diverting pulley 47, the distancebetween the hoisting rope 48 portions going to the elevator car and tothe counterweight has been somewhat increased from the widthcorresponding to the diameter of the traction sheave 2.

The machine in FIG. 6 is very much like the one illustrated by FIGS.1-4. For a practical elevator, the most important differences lie in themanner of mounting the traction sheave and in the consequent possibilityof using traction sheaves of different widths (lengths?) in the machinemore freely depending on the need defined by each elevator to beinstalled, and in the manner of implementing the bearings and the outerend of the rotating shaft. FIG. 7 shows a clear illustration of thebearings and the output end of the rotating shaft.

In the drive machine in FIG. 6, each end of the traction sheave 102 isattached to a rotor 117,118. Thus, the traction sheave is placed betweentwo rotors. In the case of an axial motor as in the present example, themost essential part of the traction sheave, i.e. the cylinder providedwith rope grooves together with the rotor magnet ring attached to thetraction sheave, remains entirely between two planes defined by the twoair gaps perpendicular to the axis of rotation. Even if the internalstructure of the motor should differ from the axial motor of the presentexample, it will be advantageous to place the traction sheave betweenthe torque generating parts. The rotors 117,118 are rotatably mountedwith bearings on the frame blocks 103,103 a, in which the stators119,120 are fixed in place, one in each frame block. The permanentmagnets of the rotors are fixed to the rotors 117,118 by a suitablemethod. The magnetic flux of the rotor passes via the rotor disc. Thus,the part of the rotor disc that lies under the permanent magnets actsboth as a part of the magnetic circuit and as a structural member of therotor. The rotor is supported on the frame blocks by relatively largebearing elements 122. The large bearing size means that the bearingelements 122 can well sustain radial forces. The bearing elements, e.g.roller bearings, are of a design that allows axial motion of themachine. Such bearings are generally cheaper than bearings that preventaxial motion, and they also permit equalization of the air gaps in thestator-rotor pairs on either side of the traction sheave. Theequalization adjustment is performed using a separate, relatively smallauxiliary bearing 140 mounted on one of the frame blocks. The auxiliarybearing 140 also receives the axial forces between the traction sheaveand the machine frame. The other frame block—need not be provided withan auxiliary bearing. The auxiliary bearing 140 is fixed to a cover 191attached to the frame block and covering the bearing space. Mounted onthe cover 191 is a resolver 190 or other device for the measurement ofangle and/or speed, supported by a supporter 189. The end 188 of therotating shaft 199 transmitting the traction sheave motion projectsthrough the central part 192 of the cover 191, and the resolver axle isattached to this shaft end. At the other end of the shaft of themachine, usually no output from the rotating shaft is needed, so asimpler cover 187 closing the bearing space is sufficient at that end.On the side facing the traction sheave, the bearing spaces are closedwith covers 186.

The traction sheave and the rotor parts are attached to each other toform the rotating part of the machine, supported by bearings on theframe blocks. As the traction sheave is connected to the rotor parts117,118 by its rim or at least by a fixing circle of a large diameter,the rotating part can be regarded as forming the drive shaft of themachine in itself. As for practical design, the deflection of such ashaft is almost nil, so the design of the bearings of the drive shaftand its suspension on the frame blocks is a fairly simple task. Theauxiliary bearing 140 and the larger bearing 122 supporting the radialforces are placed one after the other in the axial direction, which is adifferent solution as compared with the relative positions of theauxiliary bearing 40 and the larger bearing 22 in the machineillustrated by FIGS. 1-4, in which the auxiliary bearing 40 is locatedinside the larger bearing 22. The successive placement of the bearings122 and 140 allows a larger radial clearance in the bearing 122supporting the radial load than the radial clearance of the auxiliarybearing 140, because a sufficient radial flexibility can easily beachieved in the coupling between the bearings 122 and 140. Theflexibility can be increased by extending the auxiliary shaft 199connecting the auxiliary bearing 140 to the rotor part 118 by using amounting collar 197 to move the supporting point 198 of the auxiliaryshaft inwards in the machine. Additional flexibility is achieved byproviding the auxiliary shaft 199 with a waist to allow easier bendingof the shaft. In this way, the smaller play of the smaller auxiliarybearing 140 can be fully utilised. Thus, the auxiliary bearing makes itpossible to achieve an accurate axial position adjustment. Because ofthe small radial clearance, the shaft is accurately centered, which hasa favorable effect on the accuracy of the resolver signal.

The auxiliary bearing 140 is connected by its cage to the frame of themachine and by its center via the auxiliary shaft 199 to the rotatingpart formed by the traction sheave and the rotors. By adjusting themutual positions of the auxiliary shaft and the auxiliary bearing in theaxial direction of the machine, it is possible to adjust the positionsof the rotors relative to the frame. The axial adjustment may beimplemented e.g. by providing the auxiliary bearing and auxiliary shaftwith screw threads engaging each other.

It will be advantageous to adjust the air gaps between the rotors andstators of the drive machine to the same size. On the other hand, theair gaps can be adjusted until both motors/motor blocks look the same tothe electric drive. In this way, the two motors/motor blocks can bedriven by a single electric drive without incurring differences in thebehavior of the motors/motor blocks due to the drive machine beingdriven by a single electric drive. The symmetrization of themotors/motor blocks across different air gaps can also be influenced bythe mutual positions of the stators and rotors, especially by the anglesof rotation between the stators and rotors.

Several alternative methods can be used to match the motors of thedouble-motor drive machine. When matching the motors for operation inthe drive machine, the optimization can be effected by one of thefollowing methods:

i) With the motors idling, the source voltages are measured and adjustedto the same value by adjusting the air gaps and possibly also the statorangles. There are different levels in this: adjusting the amplitude ofthe fundamental wave, its amplitude and phase, additionally harmonics,and combinations of these.

ii) With no load connected to the motors, the motors are coupledtogether and the air gap and possibly also the angle of the statorpackets is adjusted so as to minimize the polyphase current. Here, too,it is possible to consider the fundamental wave and the harmonic waveseparately.

iii) With a load connected to the motors, the motors are measured andthe air gaps and possibly also the stator angles are adjusted until thecurrents in the two motors are equal. This is an advantageousalternative because any differences between the longitudinal impedancescan also be taken into account.

iv) The load is increased to the maximum and the motor currents are thenequalized by adjusting the air gaps and possibly also the stator angles.Both motors will now deliver a maximum torque and the load capacity ofthe combination is at a maximum.

In methods i) and ii), the measurements are carried out with the motoridling, thus also minimizing the energy consumption and temperaturerise.

Items i)-iv) can be suitably combined, e.g. by developing a costfunction using suitable weighting coefficients for the compensation ofmaximum load capacity, energy consumption and harmonics.

It is obvious to a person skilled in the art that the embodiments of theinvention are not restricted to the example described above, but thatthey can be varied within the scope of the following claims.

What is claimed is:
 1. A gearless elevator drive machine, comprising: atraction sheave; and an electromechanical apparatus including twoelectric motors, each having a rotor and a stator, for driving rotationof said traction sheave, wherein said traction sheave is positionedbetween the rotors of said two electric motors along an axis of rotationof said traction sheave and said traction sheave and weight appliedthereto via elevator ropes attached to an elevator car and acounterweight is, in a radial direction of the drive machine,substantially supported by bearings between stators and rotors of saidelectric motors driving said traction sheave of the drive machine. 2.The drive machine as defined in claim 1, wherein radial forces between arotating part of said traction sheave and a frame of said drive machineand axial forces in said drive machine are mainly supported by separatebearing elements.
 3. The drive machine as defined in claim 1, whereinthe traction sheave mechanically connects rotors of said two electricmotors.
 4. The drive machine as defined in claim 1, wherein saidtraction sheave is supported without a separate traction sheave axle. 5.The drive machine as defined in claim 1, wherein said traction sheave isa substantially cylindrical body with an open center and rotors of saidtwo electric motors are positioned on opposite sides of said tractionsheave.
 6. The drive machine as defined in claim 5, wherein attachmentpoints for the motors are located at the ends of the traction sheave. 7.The drive machine as defined in claim 6, wherein each end of thetraction sheave is provided with a flange on which the motor attachmentpoints are located.
 8. The drive machine as defined in claim 5, whereinthe traction sheave includes at least one flange directed to the insideof the traction sheave and provided with an attachment point for a motordriving the traction sheave.
 9. The drive machine as defined in claim 1,wherein the traction sheave has a hollow space therein surrounded bywalls, said walls passing the load applied to the drive machine from thetraction sheave to the bearings between the stators and rotors of theelectric motors.
 10. The drive machine as defined in claim 9, wherein awall of the hollow space is formed by parts of the traction sheave orthe electric motors driving the traction sheave and the ends of thehollow space are parts of the electric motors.
 11. The drive machine asdefined in claim 1, wherein an air gap is provided between the rotor andthe stator of each electric motor, such that each electric motor has anair gap associated therewith.
 12. The drive machine as defined in claim11, wherein said traction sheave is centered between the air gaps ofsaid electric motors.
 13. The drive machine as defined in claim 12,wherein the air gaps for said electric motors are the same size.
 14. Thedrive machine as defined in claim 1, wherein said two electric motorsare subjected to the same load during operation.